Unit for detecting an addition of a cleaning agent in a beverage dispenser

ABSTRACT

The present invention concerns a unit for detecting an addition of a cleaning agent in a beverage dispenser, in particular in a coffee machine. In order to guarantee that a cleaning agent has been added when automatic cleaning is carried out, a measurement device is provided as well as a method of determining whether a cleaning agent has been added to the aqueous cleaning liquid. Whether a cleaning agent has been added to the aqueous cleaning liquid can be determined in dependence upon the measured conductivity and the measured electrical resistance of the cleaning liquid, respectively.

[0001] The present invention relates to a beverage dispenser, inparticular a coffee machine, comprising a means for initiating andexecuting a cleaning process with an aqueous cleaning liquid.

[0002] The most frequent failure cause in the case of beveragedispensers used on a commercial basis, such a coffee machines used on acommercial basis, is insufficient cleaning. Al-though a regularexecution of machine cleaning processes can be guaranteed by designing asuitable control software, it is impossible to guarantee that cleaningagents will actually be used during these cleaning processes. In fullyautomatic cleaning processes, liquid cleaning agents are used, amongother substances. The cleaning agent is fed to the brewing unit at fixedtimes through a timer or in that a cleaning process is manuallytriggered by means of a pump. Such a means is complicated and expensiveand, in addition, it is difficult to super-vise the flow of the cleaningagent.

[0003] It is therefore the object of the present invention to provide abeverage dispenser in which a correct addition of cleaning agents duringthe cleaning process can be checked.

[0004] According to the present invention, this object is achieved by amethod and a measurement device for determining whether a cleaning agenthas been added to the aqueous cleaning liquid.

[0005] Due to the fact that the aqueous cleaning liquid has providedtherein a measurement device which is able to determine whether acleaning agent has been added to the aqueous cleaning liquid, a correctcleaning process can be guaranteed. If it is detected that the aqueouscleaning liquid does not contain any cleaning agent, the cleaningprocess can be discontinued, if desired. An unintentional and unnoticedexecution of an insufficient cleaning process without any cleaning agentcan be prevented in this way.

[0006] According to a preferred embodiment, the measurement device isconfigured for determining the conductivity and the electricalresistance of the cleaning liquid. If cleaning agents of any kind areadded to water, the conductivity of said water will increase markedlydue to the addition of ionizable dissolved substances. The presence ofcleaning agents in water can be measured in this way. Water containingno cleaning agent will have a resistance which is about ten times thatof water containing a cleaning agent so that, in dependence upon themeasured conductivity, it can reliably be differentiated whether or nota cleaning agent has been added to the aqueous cleaning liquid.

[0007] The measurement device preferably comprises two spaced-apartelectrodes which are arranged in the cleaning liquid. This embodiment isinexpensive and easy to realize.

[0008] The means for initiating and executing a cleaning processcomprises a control unit and a manual or an automatic feeder for thecleaning agent. According to a special embodiment, the beveragedispenser comprises a brewing unit, the measurement device beingarranged downstream of the brewing unit in an advantageous manner. Thedevice according to the present invention permits the measurement deviceto be arranged also downstream of the brewing unit, since even thepresence of e.g. coffee powder will change the conductivity of thecleaning liquid only to a minor extent so that, in spite of the presenceof coffee powder, it can be determined whether or not a cleaning agenthas been added to the cleaning liquid.

[0009] According to an advantageous embodiment, the measurement deviceis fed by a constant current source for measuring then the voltage orthe resistance between the electrodes. The measurement device can beintegrated in an LCR measuring bridge or in a voltage divider. Theelectrodes may also have applied thereto an alternating voltage or apulsed direct voltage so as to avoid oxidation and contamination.

[0010] According to a preferred embodiment, the measurement device isconnected to the control unit and the control unit is configured in sucha way that, if it is determined that no cleaning agent has been added,it will output a cleaning-process stop signal. This guarantees that nocleaning process without cleaning agent will be carried out.Furthermore, an additional indicator unit can be provided, which willthen demand an addition of cleaning agents once more. The control unitmay, however, also be configured in such a way that, when it has beendetermined that no cleaning agent has been added, the cleaning processwill be continued, the control unit comprising an error memory forstoring the absence of the cleaning agent.

[0011] Furthermore, the method according to the present inventioncomprises the step of determining at the beginning of the cleaningprocess whether a cleaning agent has been added to the cleaning liquid.The cleaning process can thus be stopped in time. According to anad-vantageous embodiment, the output signal of the measurement isdetected in analog form, e.g. as an analog voltage signal.

[0012] In the following, the present invention will be explained indetail making reference to the figures enclosed, in which:

[0013]FIG. 1 shows a schematic, simplified representation of a beveragedispenser according to the present invention.

[0014]FIG. 2 shows a device for determining whether a cleaning agent hasbeen added to an aqueous cleaning liquid.

[0015]FIG. 3 shows measurement results of various media measured by thedevice according to the present invention.

[0016]FIG. 4 shows an equivalent circuit diagram for voltagemeasurement.

[0017]FIG. 1 shows, in a greatly simplified representation, theschematic structural design of a coffee machine according to a preferredembodiment of the present invention. As can be seen in FIG. 1, thecoffee machine according to the present invention comprises awater-supply line 1 through which water is conducted into a water heater3 where it is heated. The hot water can run via a brewing line 4 into abrewing unit 5 to which coffee powder has been fed by a dosing means,which is not shown. The brewed coffee can then run via a 3/2-way valve 6either into a coffee pot 8 or it can be discharged through a dischargeline 7. Such coffee machines must be regularly cleaned with a cleaningagent. Cleaning is carried out either automatically or manually. In sodoing, cleaning agent is fed to the brewing unit via a cleaning agentfeeder 2. The cleaning process is initiated and executed by a controlunit 10. In the present embodiment, the discharge line 7 hasincorporated therein a measurement device 9 for measuring theconductivity and the electrical resistance of the cleaning liquidflowing off through the discharge line 7. As can be seen from FIG. 2,the measurement device 9 comprises two spaced-apart electrodes 9 a, 9 bwhich extend into the aqueous cleaning liquid. In the presentembodiment, the two electrodes 9 a, 9 b extend up to the centre line Mof the tube section of the discharge line 7. The electrodes may consiste.g. of titanium or of V2A steel. The electrode spacing rangespreferably from 5 to 30 mm, in the preferred embodiment it is e.g. 16mm. The size of the electrode surface ranges between 10 and 50 mm2, inthe present embodiment it is e.g. 35 mm2. The media temperature isbetween 90 and 100°.

[0018] Via the lines 12, a current is applied to the electrodes 9 a and9 b via a constant-current source or an a.c. voltage source (e.g. 100 Hzor in the KHz range), which is not shown. The control unit 10 isconnected to the measurement device 9 and interprets the measurementvalue detected by said measurement device 9 so as to find out whether ornot cleaning agent is contained. The control unit 10 is additionallyconnected to an indicator unit 11 capable of outputting an opticaland/or an acoustic signal.

[0019] At the beginning of the cleaning process, i.e. when the cleaningprocess has been initiated by the control unit 10, a measurement iscarried out by the measurement device 9. If cleaning agents of any kindare added to water, the conductivity of water increases markedly due tothe addition of ionizable dissolved substances. The presence of cleaningagents in the aqueous cleaning liquid can be measured in this way withthe aid of the two electrodes 9 a, 9 b, i.e. the ohmic resistance R ofthe measurement arrangement changes in accordance with the addition ofcleaning agents, since R=ρ×I/A (wherein ρ is the specific resistance ofthe solution, I the electrode spacing and A the effective electrodesurface). The quotient I/A is the resistance capacitance for themeasurement arrangement, which is a constant value. It follows that theconductivity of the cleaning liquid can be ascertained through themeasurement of the ohmic resistance and through the measurement of thevoltage between the electrodes 9 a and 9 b, respectively.

[0020] The output signal of the measurement device is detected in analogform by the control unit 10. The analog output signal can also beconverted into a digital signal via a threshold switch. The outputsignal of the measurement device is detected via the normal wiring forresistance measurement; the measurement device can be integrated eitherin an LCR measuring bridge or in a voltage component.

[0021]FIG. 4 shows an example for an equivalent circuit diagram forvoltage measurement. As has already been mentioned, the electrodes 9 aand 9 b are supplied with alternating voltage via lines 12 through theoscillator (I 1). In order to prevent deposits on the electrodes, analternating voltage in the KHz range, here 4 KHz, is applied to theelectrodes in this embodiment. It is also imaginable to apply a pulseddirect voltage to the electrodes. An alternating voltage will alsoprevent an oxidation of the electrodes. In FIG. 4, the resistor R2corresponds to the ohmic resistance in the measurement solution which isto be determined. The resistors R1 and R2 define a voltage divider. Thesignal from the voltage divider, whose magnitude depends, in turn, onthe conductivity of the measurement solution, is then ap-plied to avoltage follower. The voltage-divided signal is here integrated in theintegrator (I 2). The analog output signal can be converted into adigital signal via a threshold switch, or it can be evaluated directlyvia the analog input of the control unit 10. According to the presentinvention, the measurement device, for example, comprises electrodes 9a, 9 b with an electrode spacing of 16 mm and a respective electrodesurface of 35 mm2. In the case of a measured conductivity of variousdrinking waters in the range of 500 to 1000 μS, the following holdstrue:

R=L/(A*ρ)=16 mm/(35 mm²*500 μS)=914 Ω

16 mm/(35 mm²*1000 μS)=457 Ω

[0022] With the electrode dimensions chosen, a resistor of R1=180 ohm isrecommended. In the case of a voltage divider of 180 ohm to 914 ohm and457 ohm, respectively, this will, in the case of drinking water, resultin an output voltage or measurement voltage of 4.2 volts to 3.6 voltswhen a voltage of 5 volts is applied.

[0023] The control unit 10 interprets the measurement value so as tofind out whether or not cleaning agent is contained, i.e. themeasurement value is compared e.g. with reference values stored in thecontrol unit 10, whereupon it is decided whether the measurement valuecorresponds to a conductivity with or without cleaning agent. If themeasurement value corresponds to a conductivity with cleaning agent, thecleaning will be continued. If the measurement value corresponds to anelectric conductivity for a cleaning liquid without a cleaning agent,which means that a cleaning process has been initiated but no cleaningagent has been supplied to the tap water via the cleaning agent feeder2, the cleaning process will be discontinued by the control unit 10 inthat the control unit outputs a cleaning-process stop signal.Simultaneously, the control unit can pass on a signal to the indicatorunit 11 which will demand an addition of cleaning agents once more. Theindicator unit 11 can out-put an optical an/or an acoustic signal. Itis, however, also possible that the control unit 10 is configured insuch a way that, even if it is detected that no cleaning agent has beenadded to the cleaning liquid, the cleaning process will be continuednevertheless. The absence of the cleaning agent is, however, stored inan error memory, which is not shown, and, if desired, an error messagecan appear.

[0024]FIG. 3 shows the voltages between the electrodes 9 a and 9 b ofvarious media, which have been measured by the arrangement shown inFIG. 1. As can be seen from FIG. 3, the measured voltages will dropmarkedly, when a cleaning agent is added to the cleaning liquid. Apossible presence of coffee powder in the brewing unit 5 will notcorrupt the measurement result, since the respective voltage measured ismarkedly higher than the voltages measured in the presence of cleaningagents. Only a very large amount of coffee corresponding to 26 g ofcoffee powder will reduce the measured voltage to such an extent that itcorresponds to a range which is equal to the conductivity range ofcleaning liquid with cleaning agent. This will, however, not interferewith the measurement, since 26 g of coffee powder exceed the normalamount of coffee powder by far. Such large amounts will not be used inpractice and, if this should actually be the case, the control unitwould indicate a malfunction of the motor of the brewing unit so thatthe cleaning process could not even be started.

[0025] Summarizing, it should therefore be stated that the beveragedispenser according to the present invention as well as the methodaccording to the present invention permit reliable cleaning.

1. A beverage dispenser comprising a means (10, 2) for initiating andexecuting a cleaning process with an aqueous cleaning liquid,characterized by a measurement device (9) for determining whether acleaning agent has been added to the aqueous cleaning liquid during thecleaning process.
 2. A beverage dispenser according to claim 1,characterized in that the measurement device (9) is configured fordetermining the conductivity and the electrical resistance of thecleaning liquid, respectively.
 3. A beverage dispenser according toclaim 2, characterized in that the measurement device (9) comprises twospaced-apart electrodes (9 a, 9 b) which are arranged in the cleaningliquid.
 4. A beverage dispenser according to one of the claims 1 to 3,characterized in that the means (10, 2) for initiating and executing acleaning process comprises a control unit (10).
 5. A beverage dispenseraccording to at least one of the claims 1 to 4, characterized in thatthe means for initiating and executing a cleaning process comprises amanual or automatic feeder for the cleaning agent.
 6. A beveragedispenser according to at least one of the claims 1 to 5, characterizedin that the beverage dispenser comprises a brewing unit (5).
 7. Abeverage dispenser according to claim 6, characterized in that themeasurement device (9) is arranged downstream of the brewing unit (5).8. A beverage dispenser according to at least one of the claims 1 to 7,characterized in that the measurement device (9) is fed by a constantcurrent source.
 9. A beverage dispenser according to at least one of theclaims 1 to 8, characterized in that the measurement device (9) isintegrated in an LCR measuring bridge or in a volt-age divider.
 10. Abeverage dispenser according to claim 3, characterized in that an a.c.voltage source applies an alternating voltage to the electrodes (9 a, 9b).
 11. A beverage dispenser according to claim 3, characterized in thatthe electrodes (9 a, 9 b) have applied thereto a pulsed direct voltage.12. A beverage dispenser according to claim 4, characterized in that themeasurement device (9) is connected to the control unit (10) and thatthe control unit (10) is config-ured in such a way that, if it isdetermined that no cleaning agent has been added, it will output acleaning-process stop signal.
 13. A beverage dispenser according toclaim 12, characterized in that the control unit (10) is additionallyconnected to an indicator unit (11) which demands an addition ofcleaning agents once more.
 14. A beverage dispenser according to claim4, characterized in that the control unit (10) comprises an error memoryfor storing the absence of the cleaning agent.
 15. A method of cleaninga beverage dispenser with an aqueous cleaning liquid, characterized inthat by means of a measurement device, it is determined whether acleaning agent has been added to the aqueous cleaning liquid.
 16. Amethod according to claim 15, characterized in that the step ofdetermining whether a cleaning agent has been added to the aqueouscleaning liquid is carried out in de-pendence upon the measuredconductivity and the measured electrical resistance of the aqueouscleaning liquid, respectively.
 17. A method according to claim 16,characterized in that the measurement is executed via two electrodeswhich have a direct voltage or a pulsed direct voltage or an a.c.volt-age applied thereto.
 18. A method according to one of the claims 15to 17, characterized in that the output sig-nal of the measurement isdetected in analog form.
 19. A method according to one of the claims 15to 18, characterized in that the step of determining whether a cleaningagent has been added to the cleaning liquid is carried out at thebeginning of the cleaning process.
 20. A method according to one of theclaims 15 to 19, characterized in that, when it has been determined thatno cleaning agent has been added, the cleaning process is dis-continuedand an addition of cleaning agent is demanded once more.
 21. A methodaccording to one of the claims 15 to 20, characterized in that, when ithas been determined that no cleaning agent has been added, the cleaningprocess is con-tinued, the absence of the cleaning agent being, however,stored in an error memory.